fix: Yarn switch install support and tests (#761)

Author: aduh95

sources/commands/Enable.ts

@@ -83,9 +83,9 @@ export class EnableCommand extends Command<Context> {
     const symlink = path.relative(installDirectory, path.join(distFolder, `${binName}.js`));
 
     if (fs.existsSync(file)) {
-      const currentSymlink = await fs.promises.readlink(file);
+      const currentSymlink = await fs.promises.realpath(file);
 
-      if (binName.includes(`yarn`) && corepackUtils.isYarnSwitchPath(await fs.promises.realpath(file))) {
+      if (binName.includes(`yarn`) && corepackUtils.isYarnSwitchPath(currentSymlink)) {
         console.warn(`${binName} is already installed in ${file} and points to a Yarn Switch install - skipping`);
         return;
       }

tests/Enable.test.ts

@@ -93,14 +93,14 @@ describe(`EnableCommand`, () => {
       await xfs.writeFilePromise(ppath.join(cwd, `yarn`), `hello`);
 
       process.env.PATH = `${npath.fromPortablePath(cwd)}${delimiter}${process.env.PATH}`;
-      await expect(runCli(cwd, [`enable`])).resolves.toMatchObject({
+      await expect(runCli(cwd, [`enable`, `--install-directory`, npath.fromPortablePath(cwd)])).resolves.toMatchObject({
         stdout: ``,
         stderr: ``,
         exitCode: 0,
       });
 
       const file = await xfs.readFilePromise(ppath.join(cwd, `yarn`), `utf8`);
-      expect(file).toBe(`hello`);
+      expect(file).not.toBe(`hello`);
     });
   });
 
@@ -109,15 +109,15 @@ describe(`EnableCommand`, () => {
       await xfs.mkdirPromise(ppath.join(cwd, `switch/bin`), {recursive: true});
       await xfs.writeFilePromise(ppath.join(cwd, `switch/bin/yarn`), `hello`);
 
-      await xfs.linkPromise(
+      await xfs.symlinkPromise(
         ppath.join(cwd, `switch/bin/yarn`),
         ppath.join(cwd, `yarn`),
       );
 
       process.env.PATH = `${npath.fromPortablePath(cwd)}${delimiter}${process.env.PATH}`;
-      await expect(runCli(cwd, [`enable`])).resolves.toMatchObject({
+      await expect(runCli(cwd, [`enable`, `--install-directory`, npath.fromPortablePath(cwd)])).resolves.toMatchObject({
         stdout: ``,
-        stderr: ``,
+        stderr: expect.stringMatching(/^yarn is already installed in .+ and points to a Yarn Switch install - skipping\n$/),
         exitCode: 0,
       });